Cumnor: Petrol in a Diesel Car? How Worried to Be
If it has not been started, worry less than you likely are. Till the ignition primes the pump, your starter turns, or the car is driven, petrol in a diesel tank just sits there and does nothing. Which means the honest reply to that first Cumnor question — "have I wrecked it?" — normally no. To leave the car that way, ring Petrol in Diesel then leave your motor switched off. Further down, you will find what petrol really does inside a diesel, how far it might have gone, and how to stop it happening to you a second time.
Petrol in a diesel: what does it do to the motor?
Diesel has two tasks on its way through a motor. It lubricates first, and only then does it burn. What stops the surfaces inside the high-pressure fuel pump and the fuel injectors from wearing down against each other is your diesel passing through them — they are built to extremely fine tolerances.
Petrol does the first job badly and the second not at all. Being less viscous than diesel, petrol strips away the lubrication a fuel system needs, leaving a pump on the mixture wearing itself. It is also made to resist igniting under compression — the reverse of what a diesel needs — which is where you get the knocking.
The shape of the issue is clear when you put those together. Not contact but circulation is what does the damage. Where the petrol is only in the tank, it's a problem of fuel, nothing more. The start of a mechanical problem is a pump that has been labouring on that petrol — and whatever a worn pump sheds moves on with your fuel to the injectors beyond it.
How serious is petrol in a diesel? Four situations our engineers see in Cumnor
The best case there can be: filled up, not once started. At a forecourt, and genuinely only there, that petrol is still limited to the tank — because everywhere else the car was driven to get to it. The job is emptying and rinsing on the spot.
Your ignition turned on, or a brief start. The system has been primed, so petrol has left your tank and got to the fuel filter and the fuel lines. Usually little more than emptying, rinsing and seeing to your filter, and so still simple.
Driven a couple of miles. Now the pump has spent those miles labouring on diluted fuel. Distance is only half of it; how hard it was driven matters equally. Either way this work includes that tank, the fuel lines, your filter and clean fuel through the whole system. Short trips, such as the school run to Cumnor Church of England School (Voluntary Controlled), are one thing. A run as far as Oxford, under 5 miles away, is a very different task. So is any distance on the Wheatley Spur, under 10 miles from Cumnor, where the motor has been running hard the whole time.
It complained, and only then stopped: smoke, clattering, a throttle gone soft, an idle gone lumpy. What you are hearing is the engine signalling fuel that no longer behaves like diesel. Whether it is the verge on B4017, a lay-by or a side street, stop there and leave it. Long-term damage is very uncommon if a car is pulled over soon, and the fuel drain and flush that still come first take care of it.
Cumnor people and the petrol in a diesel myths they hear
Myth: "Fill it the rest of the way with diesel and it will be fine." It will not. Topping up removes nothing; it gives you a fuller tank of the same mixture. That advice supposes a diesel fuel system tolerates petrol by percentage. It doesn't.
Myth: a newer diesel copes with a bit of petrol. If anything, the opposite. At higher pressure, through smaller components: that is how a current diesel handles its fuel, and so the protection counts more, not less.
"It starts, it drives, so no harm done" — the myth that trips up most motorists than any other. Feed diesel to a petrol engine and it generally will not run, and so the driver stops — and the harm stops with them. Nothing looks to have happened when a diesel fed petrol fires up, ticks over and drives away, which it usually does; meanwhile the pump wears. Being able to run is not the same as being fine.
Myth: a two-stroke additive lets you to drive home. It was an old fix, supposed for another problem. None of what petrol weakened gets put back by it — and afterwards, the tank still holds that petrol.
Myth: "Drain the tank yourself and you are sorted." After the engine has run, some of that petrol is no longer inside that tank: it's in the filter and the fuel lines, and it goes straight back through the pump on the next start. Emptying petrol into a can at the kerbside is also truly dangerous.
How does petrol in a diesel happen?
Nobody does it on purpose, and it is seldom carelessness. The petrol nozzle is the smaller of the two and slips into a diesel filler with almost no resistance; a diesel nozzle mostly will not go into a petrol vehicle at all. The forecourt makes it simple, and the error runs one way.
When habit and the vehicle stop matching, it happens. A new motor, a hire car or a courtesy car. Two motors on one driveway, one petrol, one diesel. Your normal forecourt, its pumps suddenly in a different order. A train to catch, and a hurried fill en route to Oxford. The first fill-up in a diesel Volkswagen Tiguan after years of driving petrol is precisely the moment it happens. With rain, a call arriving, or a car full of children to deal with, the hand just does what it always has.
How to prevent petrol in a diesel on your next fill-up in Cumnor
- The label is what counts, so read the petrol pump instead of the colour: in the UK unleaded handles are normally green and diesel black, yet not on every forecourt.
- Many cars state the fuel type inside your filler flap or on the cap, so check it on the first fill in a vehicle you don't know.
- One of each in the home? Label your key to your diesel — a bright fob, a sticker — since intending to remember is not enough.
- Before the nozzle leaves the pump the first time you fill a hired or new vehicle, say "diesel" out loud. Daft, yes, yet it does the trick.
- Thinking about something else is when this becomes an easy mistake to make, and so put your phone away then keep your mind on the pump.
- A misfuel inhibitor helps, up to a point. Some diesels have a filler designed to block a petrol nozzle, and add-on devices are available for motors without one. They are a backstop, not a reason to stop checking the petrol pump.
- As soon as you realise, stop: less petrol in that tank means a weaker blend. What to do next does not change, though — still do not start the vehicle.
Petrol already in a diesel around Cumnor? Begin here
Then, there is only a short order of things. Starting it is out, and so is switching on the ignition. Ask the staff to help you roll it clear of the pump if you're still at the forecourt, whether that is the nearest petrol station or anywhere else. What was put in, roughly how much, and whether it's run: tell us that when you phone 0333 366 0103.
Say so if it was AdBlue instead of petrol: it's a different problem, with its own page for Cumnor, since AdBlue brings corrosion and deposits instead of lost lubrication.
One petrol in a diesel job in Cumnor costs more than another. Why?
The four scenarios above are four different tasks, so no single price for this would be honest. Chiefly, the cost shifts with which one you are in. The share matters next, meaning how much of your tank is petrol, followed by the position of the vehicle and whether getting to it is safe for our van.
Three queries come first, before any quote, rather than after — what was put in, how much, has it run — and this is the reason. Those answers are what turn a range into one firm number.
About Cumnor itself
Cumnor is a village in Oxfordshire, situated approximately 3.5 miles west of Oxford, and is characterized by its predominantly detached housing stock. Cumnor sits in a rural area at an elevation of around 111 metres, near the villages of Chawley, Eaton, and Filchampstead. Cumnor is a relatively small community with a population of around 1113 residents, and is located about 54 miles from London.
Cumnor and Oxfordshire: where our fuel drain cover reaches
Cumnor sits in the OX postcode area, and our vans that answer petrol in diesel jobs there work the spots around it as well — Chawley, Eaton and Filchampstead among them. A forecourt, a supermarket car park, a lay-by or your own drive are all spots our technicians work, and the vehicle does not need to move to us.
Cumnor: still at the pump?
Then you're in the best spot there is. Switched off it stays; then ring.